edit: (LOL, disregard that. I just remembered that my Angband repo is on 4.0.5! I recall Nick changed stealth when he changed pathfinding)
edit2: (It seems he changed it back? well, then the description below is correct)

Player's noise is 1 << (30 - stealth). In other words, noise is 2 in the power of (30 - stealth).